Organic light emitting display device and method for manufacturing the same

ABSTRACT

Disclosed are an organic light emitting display device capable of achieving an intra-pixel integration design with sufficient storage capcacitance and a method for manufacturing the same in which the organic light emitting display device includes a first active layer connected to the driving gate electrode and the data line while crossing the gate line, and a second active layer spaced apart from the first active layer while overlapping the driving gate electrode and being connected to the current drive line and storage electrode.

This application claims the benefit of Korean Patent Application No.10-2015-0120071, filed on Aug. 26, 2015, which is hereby incorporated byreference as if fully set forth herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an organic light emitting displaydevice, and more particularly to an organic light emitting displaydevice capable of achieving an intra-pixel integration design withsufficient storage capcacitance and a method of manufacturing the same.

Discussion of the Related Art

With the recent development of various portable electronic appliancessuch as mobile communication terminals and notebook computers, demandfor flat panel display devices applicable to portable electronicappliances is increasing.

Examples of flat panel display devices being currently researchedinclude a liquid crystal display device, a plasma display device, afield emission display device, and an organic or inorganic lightemitting diode display device. In particular, in the case of the organiclight emitting display device, the application field thereof is beingexpanded by virtue of its various advantages such as advancedtechnologies for mass production, easy implementation of driving means,low power consumption, high picture quality, realization of a largescreen, and flexibility.

Such an organic light emitting device includes an organic light emittingdiode in each pixel for light emission and a pixel circuit forcontrolling current flowing through the organic light emitting diode.The pixel circuit typically includes at least two thin film transistors,and a storage capacitor.

Meanwhile, thin film transistors are classified into a thin filmtransistor having a top gate structure and a thin film transistor havinga bottom gate structure.

For formation of thin film transistors (TFTs) having a top gatestructure, an amorphous silicon layer is first formed over a substrate.The amorphous silicon layer is then crystallized using an excimer layerand, as such, is formed into a polysilicon layer. A photoresist film(not shown) is subsequently coated over the crystallized polysiliconlayer. The photoresist film is subjected to a light exposure anddevelopment to form a photoresist film pattern. Using the photoresistfilm pattern as a mask, the polysilicon layer is then etched, to leavean active layer in regions each corresponding to a desired portion ofeach pixel. A gate insulating film is then formed to cover the activelayer. Gate electrodes are finally formed on the gate insulating film,to correspond to the active layer.

On the other hand, formation of TFTs having a bottom gate structure iscarried out in such a manner that formation of an active layer and gateelectrodes is reverse to that of the TFTs having a top gate structure.Meanwhile, the crystallization process for crystallizing amorphoussilicon into polysilicon is carried out at a temperature of 400° C. ormore and, as such, disconnection of the active layer may occur duringthe crystallization process in the bottom gate structure. For thisreason, recently developed organic light emitting display devices preferTFTs having a top gate structure in which gate electrodes are formedafter completion of crystallization, in order to eliminate the problemof active layer disconnection.

Hereinafter, one pixel of a conventional organic light emitting displaydevice including TFTs having a top gate structure will be described withreference to the accompanying drawings.

FIG. 1 is a circuit diagram illustrating one pixel of a conventionalorganic light emitting display device. FIG. 2 is a cross-sectional viewtaken along a line passing through a drive transistor and a switchingTFT, which are illustrated in FIG. 1.

FIG. 1 illustrates a configuration of a pixel circuit in an organiclight emitting display device having a basic structure. The pixelcircuit includes a switching TFT ST, a drive TFT DT connected to theswitching TFT ST, and an organic light emitting diode OLED connected tothe drive TFT DT.

The switching TFT ST is formed at a region where a gate line GL and adata line DL cross each other. The switching TFT ST functions to selecta pixel. As illustrated in FIG. 2, the switching TFT ST includes aswitching gate electrode SG 10 protruding from the gate line GL, aswitching source electrode SS branched from the data line DL, aswitching drain electrode SD 45, and a first active layer 60 having aswitching channel region.

In this case, the switching channel region, which is designated byreference numeral 60 a, is defined by a portion of the first activelayer 60 overlapping the switching gate electrode SG. Portions of thefirst active layer 60 disposed at opposite sides of the switchingchannel region 60 a are doped with impurity ions and, as such, functionas a source region 60 b and a drain region 60 c, respectively. Thesource region 60 b and drain region 60 c are connected to the switchingsource electrode SS and switching drain electrode SD of the switchingTFT ST, respectively.

Meanwhile, the drive TFT DT functions to drive the organic lightemitting diode OLED of the pixel selected by the switching TFT ST. Thedrive TFT DT includes a driving gate electrode DG 15 connected to theswitching drain electrode SD of the switching TFT ST, a drive sourceelectrode DS included in a reference voltage line RL, a drivingelectrode pattern DD 55 spaced apart from the drive source electrode DS,and a second active layer 70 having a driving channel region 70 a andsource and drain regions 70 b and 70 c respectively connected to thedrive source electrode DS and driving electrode pattern DD 55 around thedriving channel region 70 a. The driving electrode pattern DD of thedrive TFT DT is connected to a first electrode of the organic lightemitting diode OLED.

The driving gatedriving gate electrode DG 15 is arranged over theswitching TFT ST and beneath the drive TFT DT while overlapping theswitching drain electrode 45 and driving electrode pattern,respectively. Electrical connection is provided at overlapping portionsof the driving gate electrode DG 15 and switching drain electrode 45and, as such, the drain electrode of the switching TFT ST and the gateelectrode of the drive TFT DT are connected.

In addition, a storage capacitor Cst may be defined by the overlappingportions of the driving gate electrode DG 15 and driving electrodepattern 55 of the drive TFT DT.

In the conventional organic light emitting display device, the switchingdrain electrode SD and driving gate electrode DG, which are formed tohave a straight shape on a planar surface, overlap each other on theplanar surface for a connection between the drain electrode of theswitching TFT and the gate electrode of the drive TFT. The switchingdrain electrode SD and the driving gate electrode DG have an elongatedplanar straight electrode shape. In this case, the driving electrodepattern DD 55 used as one electrode of the storage capacitor Cst isbeneficially not be connected to the driving gate electrode DG 15 eventhough the driving electrode pattern DD 55 overlaps the driving gateelectrode DG 15 when viewed in plan. Accordingly, at least the drivinggate electrode DG 15 and the connection portions of the second activelayer 70 and driving electrode pattern 55 are spaced apart from eachother when viewed in plane. Since the driving gate electrode DG 15maintains a planar spacing from the connection portions of the secondactive layer 70 and driving electrode pattern DD 55, the overlap areabetween the driving electrode pattern DD 55 and the driving gateelectrode DG 15 is small. As a result, the storage capacitancedetermined by the overlap area may be insufficient.

Meanwhile, development of organic light emitting display devices isbeing accelerated to satisfy demand for large area and high densitydisplays in accordance with gradual expansion of application fieldsthereof. In particular, as resolution increases, the size of the unitpixel is decreased. The decrease in unit pixel size means that the spaceof the unit pixel where TFTs and a storage capacitor are arranged isreduced. In the above-mentioned conventional organic light emittingdisplay device, the pixel size may need to be increased to secure asufficient storage capacitor area. For this reason, it may be difficultto simultaneously secure both high resolution and sufficient capacity ofa storage capacitor.

Meanwhile, the organic light emitting diode OLED is formed through alamination of a first electrode connected to the drain electrode DD 55of the drive TFT DT, organic layers including an organic light emittinglayer, and a second electrode.

In addition, the inter-pixel position of the organic light emittingdiode may vary in accordance with light emission types. For example, ina top emission type, the organic light emitting diode can emit light atthe top side thereof, irrespective of overlap thereof with a pixelcircuit including light-shielding metal wirings. In a bottom emissiontype, however, the light-shielding metal wirings may shield emission oflight and, as such, the aperture ratio of the organic light emittingdiode may be reduced as the area of the pixel circuit increases.

In the above-mentioned conventional organic light emitting displaydevice having a top gate structure, the switching drain electrode anddriving gate electrode, which are connected in one direction, arebeneficially arranged between the active layers of the switching TFT anddrive TFT spaced apart from each other when viewed in plane. For thisreason, it may be difficult to achieve a desired intra-pixel circuitintegration. Accordingly, the conventional organic light emittingdisplay device having a top gate structure may need to secure a spacebetween intra-pixel circuit regions, which makes it difficult to securehigh resolution.

In addition, due to the features of the top gate structure, the gateelectrode layer occupying a relatively small area in the pixel area isarranged over the active layer and, as such, it may be difficult tosecure an area for a storage capacitor. That is, it may be difficult tosecure an area overlapping the gate metal layer having a small area forthe storage capacitor to have sufficient capacity.

SUMMARY

Accordingly, the present invention is directed to an organic lightemitting display device and a method for manufacturing the same thatsubstantially obviate one or more problems due to limitations anddisadvantages of the related art.

An advantage of the present invention is to provide an organic lightemitting display device capable of achieving an intra-pixel integrationdesign with sufficient storage capcacitance.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, anorganic light emitting display device may, for example, include a gateline and a data line crossing each other on a substrate, a sensing lineextending in parallel to the gate line, and a current driving line and areference voltage line extending in parallel to the data line, a storagecapacitor provided by an overlap between a storage electrode and adriving gate electrode, wherein the storage electrode and the drivinggate electrode are disposed on different layers, respectively, a firstactive layer crossing the gate line, wherein opposite ends of the firstactive layer connected to the driving gate electrode and the data lineand a second active layer spaced apart from the first active layer whileoverlapping the driving gate electrode, wherein the second active layerprotruding from the driving gate electrode has opposite side portionsrespectively connected to the current drive line and the storageelectrode.

The second active layer may extend from the portion connected to thestorage electrode such that the second active layer is connected to thereference voltage line while crossing the sensing line.

The first and second active layers may be arranged on the same layer,the driving gate electrode is arranged beneath the first and secondactive layer and the storage electrode is arranged beneath the drivinggate electrode.

The organic light emitting display device may further comprise aswitching electrode pattern arranged over the first active layer in aregion where the first active layer and the driving gate electrodeoverlap each other.

And, the switching electrode pattern may penetrate through one end ofthe first active layer such that the switching electrode pattern isconnected to an upper surface of the driving gate electrode while beinglaterally connected to the first active layer. Also, first active layerhas a first switching channel region at a portion thereof overlappingthe gate line and a first switching thin film transistor is defined bythe gate line, the first active layer, the switching electrode patternlaterally connected to one end of the first active layer, and the dataline connected to the other end of the first active layer.

Furthermore, the organic light emitting display device may furthercomprise a driving electrode pattern arranged over the second activelayer, wherein the driving electrode pattern does not overlap with thedriving gate electrode while overlapping the storage electrode.

Furthermore, the driving electrode pattern penetrates through the secondactive layer, wherein the driving electrode pattern is connected to anupper surface of the storage electrode is laterally connected to thesecond active layer, the second active layer has a driving channelregion at a portion thereof overlapping the driving gate electrode; anda drive thin film transistor is defined by the driving gate electrode,the second active layer, the current driving line connected to thesecond active layer, and the driving electrode pattern.

The organic light emitting display device may further comprise anauxiliary driving gate electrode connected to the switching electrodepattern while overlapping the driving gate electrode.

And, the gate line and the sensing line may be arranged over the firstactive layer and the second active layer, respectively and the dataline, the reference voltage line and the current driving line may bearranged over the gate line and the sensing line.

The auxiliary driving gate line may be arranged at the same layer as thegate line while partially overlapping the second active layer.

Further, the lateral connection between the switching electrode patternand the first active layer may be provided in a doped region of thefirst active layer and the lateral connection between the drivingelectrode pattern and the second active layer may be provided in a dopedregion of the second active layer.

The organic light emitting display device further comprises a bank fordefining a light emission area and an organic light emitting diodecomprising a first electrode connected to the driving electrode pattern,a light emitting layer arranged in the light emission area, and a secondelectrode arranged on the light emitting layer.

Meanwhile, the light emission area may completely overlap the storagecapacitor.

Also, an organic light emitting display device according to a differentembodiment may, for example, include a substrate having a plurality ofpixels in a matrix, a storage electrode at each of the pixels on thesubstrate, a driving gate electrode over the storage electrode via afirst interlayer insulating film wherein the driving gate electrodeoverlaps the storage electrode, to define a storage capacitor, first andsecond active layers over the driving gate electrode via a gateinsulating film, wherein the first and second active layers are spacedapart from each other while overlapping the driving gate electrode andthe storage electrode, respectively, a gate line and a sensing line overthe first active layer via a second gate insulating film extending inparallel, to cross the first and second active layers, a data line, acurrent driving line and a reference voltage line extending in adirection crossing the gate line, arranged over the gate line and thesensing line via a second interlayer insulating film while, wherein thedata line is connected to one end of the first active layer, the currentdriving line and the reference voltage line are connected to oppositeends of the second active layer, respectively and a switching electrodepattern and a driving electrode pattern arranged on a second interlayerinsulating film, wherein the switching electrode pattern and the drivingelectrode pattern are disposed on the same layer as the data line, theswitching electrode pattern is connected to the other end of the firstactive layer, and the driving electrode pattern is connected to aportion of the storage electrode protruding from the driving gateelectrode.

In this case, the organic light emitting display device further comprisean auxiliary driving gate electrode arranged on the second gateinsulating film overlapping the driving gate electrode, wherein theauxiliary driving gate electrode is connected to the switching electrodepattern.

Furthermore, a method for manufacturing an organic light emittingdisplay device may, for example, include preparing a substrate having aplurality of pixels in a matrix, forming a storage electrode at each ofthe pixels on the substrate, forming a driving gate electrode over thestorage electrode via a first interlayer insulating film such that thedriving gate electrode overlaps the storage electrode, to define astorage capacitor, forming first and second active layers over thedriving gate electrode via a gate insulating film such that the firstand second active layers are spaced apart from each other whileoverlapping the driving gate electrode and the storage electrode,respectively, forming a gate line and a sensing line over the firstactive layer via a second gate insulating film such that the gate lineand the sensing line extend in parallel, to cross the first and secondactive layers and forming a data line, a current driving line and areference voltage line over the gate line and the sensing line via asecond interlayer insulating film such that the data line, the currentdriving line and the reference voltage line extend in a directioncrossing the gate line, the data line is connected to one end of thefirst active layer, and the current driving line and the referencevoltage line are connected to opposite ends of the second active layer,respectively, and forming a switching electrode pattern and a drivingelectrode pattern in the same layer as the data line on a secondinterlayer insulating film, wherein the switching electrode pattern isconnected to the other end of the first active layer, and the drivingelectrode pattern is connected to a portion of the storage electrodeprotruding from the driving gate electrode.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andalong with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a circuit diagram illustrating one pixel of a conventionalorganic light emitting display device;

FIG. 2 is a cross-sectional view taken along a line passing through adrive transistor and a switching thin film transistor (TFT), which areillustrated in FIG. 1;

FIG. 3 is a circuit diagram illustrating one pixel of an organic lightemitting display device according to an embodiment of the presentinvention;

FIG. 4 is a plan view illustrating one pixel of an organic lightemitting display device according to a first embodiment of the presentinvention;

FIG. 5 is a cross-sectional view taken along line I-I′ in FIG. 4;

FIG. 6 is a flowchart illustrating a procedure of manufacturing anorganic light emitting display device according to an embodiment of ofthe present invention;

FIG. 7 is a plan view illustrating one pixel of an organic lightemitting display device according to a second embodiment of the presentinvention;

FIG. 8A is a cross-sectional view taken along line II-II′ in FIG. 7;

FIGS. 8B and 8C are cross-sectional views illustrating embodimentsmodified from the second embodiment;

FIG. 9 is a graph depicting V_(g)-I_(d) characteristics exhibited when adrive has a top gate structure and when the drive TFT has a bottom gatestructure; and

FIG. 10 is a graph depicting V_(d)-I_(d) characteristics exhibited whenthe drive. TFT has a top gate structure and when the drive TFT has abottom gate structure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.Throughout the disclosure, the same reference numerals designatesubstantially the same constituent elements. In describing the presentinvention, moreover, the detailed description will be omitted when aspecific description of publicly known technologies to which theinvention pertains is judged to obscure the gist of the presentinvention. In addition, names of constituent elements used in thefollowing description are selected for easy understanding of the presentinvention, and may differ from names of practical products.

As mentioned above, in a bottom gate structure, an active layer isformed along a taper portion of a gate electrode, and crystallinecomponents of the active layer are agglomerated during thecrystallization of the active layer, thereby causing the active layer tobe disconnected at the taper portion of the gate electrode. As such, atop gate structure used in the above-mentioned conventional organiclight emitting display device to reduce or prevent such a disconnection.

The inventors of the present invention have filed Korean PatentApplication No. 10-2015-0067321, which is directed to addressing such anactive layer disconnection by changing the shape of a gate electrode ina bottom gate structure.

In an embodiment of the present invention, a driving gate electrodehaving a bottom gate structure has a gentle slope at a side portionthereof, in order to solve a disconnection of crystalline components ofan active layer at a tapered portion of the gate electrode whilesecuring a sufficient area for a storage capacitor. As a result, aneffective circuit region is secured in a pixel area with increasedintegration degree and high resolution.

FIG. 3 is a circuit diagram illustrating one pixel of an organic lightemitting display device according to an embodiment of the presentinvention.

First, one pixel of the organic light emitting display device accordingto an embodiment of the present invention will be described inconjunction with a circuit configuration thereof. As illustrated in FIG.3, the pixel includes a first switching thin film transistor (TFT) SW1arranged between a gate line SL and a data line DL, a drive TFT D-TFTconnected between the switching TFT SW1 and a current driving line VDL,a second switching TFT SW2 connected between the drive TFT D-TFT and areference voltage line RL, a storage capacitor Cst connected between aconnection point between the first switching TFT SW1 and the drive TFTD-TFT, namely, a first node A, and a connection point between the driveTFT D-TFT and the second switching TFT SW2, namely, a second node B, andan organic light emitting diode OLED arranged between the second node Band a ground terminal. A pixel area of the pixel is defined between thegate line GL and the data line DL, which cross each other. Pixel areasare arranged in a matrix on a substrate (“100” in FIG. 5).

Meanwhile, a switching drain electrode SD1 of the first switching TFTSW1 and a driving gate electrode DG of the drive TFT D-TFT are connectedto the first node A. A driving electrode pattern DD of the drive TFTD-TFT and a second switching drain electrode SD2 of the second switchingTFT SW2 are connected to the second node B.

Respective gate electrodes SG1 and SG2 of the first and second switchingTFT's SW1 and SW2 are connected to the gate line GL and a sensing lineSSL.

The first switching TFT SW1 selects a corresponding one of pixels, whichis driven in accordance with a signal applied to the gate line GL. Thedrive TFT D-TFT, which is connected to the first switching TFT SW1,controls a drive current of the selected pixel, and supplies thecontrolled drive current to the organic light emitting diode OLED.Meanwhile, the storage capacitor Cst maintains a voltage supplied fromthe first switching TFT SW1, for one frame, and, as such, the drive TFTD-TFT is maintained at a predetermined voltage. To this end, the storagecapacitor Cst is arranged between the driving gate electrode DG of thedrive TFT D-TFT and the driving electrode pattern DD. In this case, thestorage capacitor Cst, which is connected to the second switching TFTSW2, supplies, to the second node B, an initialization voltage suppliedfrom the reference voltage line RL while the second switching TFT SW2 isturned on in accordance with supply of a sensing signal from the sensingline SSL. This means that initialization is achieved in accordance withapplication of the sensing signal from the sensing line SSL in aspecific period.

A First Embodiment

FIG. 4 is a plan view illustrating one pixel of an organic lightemitting display device according to a first embodiment of the presentinvention. FIG. 5 is a cross-sectional view taken along line I-I′ inFIG. 4.

Hereinafter, the organic light emitting display device according to thefirst embodiment of the present invention, which has the circuitconfiguration of the above-described organic light emitting displaydevice, will be described with reference to FIGS. 4 and 5. The organiclight emitting display device according to the first embodiment of thepresent invention has the same electrical connection configuration asthe above-described circuit configuration, except for planar andcross-sectional arrangements thereof.

As illustrated in FIGS. 4 and 5, one pixel area of the organic lightemitting display device according to the first embodiment of the presentinvention may be defined by a gate line GL and a data line DL, whichcross each other.

In each pixel area of the organic light emitting display device, asensing line SSL is arranged in parallel to the gate line, and a currentdriving line VDL and a reference voltage line RL are arranged inparallel to the data line DL. The organic light emitting display deviceincludes, in each pixel area, a storage capacitor Cst defined by astorage electrode 110 and a driving gate electrode 120, which arearranged on different layers in the pixel area while overlapping eachother, a first active layer 130 connected, at opposite ends thereof, tothe driving gate electrode 120 and the data line DL, and a second activelayer 140 spaced apart from the first active layer 130 while overlappingthe driving gate electrode 120. The second active layer 140 has oppositeside portions connected to the current drive line VDL and the storageelectrode 110 while protruding laterally from the driving gate electrode120.

In this case, the second active layer 140 extends from a portion thereofconnected to the storage electrode 110 while crossing the sensing lineSSL, and, as such, is connected to the reference voltage line RL.

The first and second active layers 130 and 140 are arranged on the samelayer. The driving gate electrode 120 is arranged beneath the first andsecond active layers 130 and 140. The storage electrode 110 is arrangedbeneath the driving gate electrode 120.

The organic light emitting display device further includes, in eachpixel area, a switching electrode pattern 160 arranged over the firstactive layer 130 in a region where the first active layer 130 anddriving gate electrode 120 overlap each other. The switching electrodepattern 160 corresponds to the node A in the circuit of FIG. 3. Theswitching electrode pattern 160 itself functions as a drain electrode ofa first switching TFT SW1. The first switching TFT SW1 is connected tothe switching electrode pattern 160, together with a drive TFT D-TFT anda storage capacitor Cst.

The switching electrode pattern 160 extends through one end of the firstactive layer 130 while being laterally connected to the first activelayer 130. The switching electrode pattern 160 is also connected to anupper surface of the driving gate electrode 120. Thus, electricalconnection among the driving gate electrode 120, first active layer 130and switching electrode pattern 160 is provided.

The organic light emitting display device further includes, in eachpixel area, a driving electrode pattern 170 arranged over the secondactive layer 140 such that the driving electrode pattern 170 overlapsthe storage electrode 110 without overlapping the driving gate electrode120. In this case, the driving electrode pattern 170 extends through thesecond active layer 140 while being laterally connected to the secondactive layer 140. The driving electrode pattern 170 is also connected toan upper surface of the storage electrode 110. Thus, electricalconnection among the storage electrode 110, second active layer 140 anddriving electrode pattern 170 is provided. In this case, the drive TFTD-TFT is defined by the driving gate electrode 120, the second activelayer 140, which has a driving channel region 140 a at a portion thereofoverlapping the driving gate electrode 120, the current driving line VDLconnected to the second active layer 140, and the driving electrodepattern 170. The storage capacitor Cst is formed between the drive TFTD-TFT and the switching electrode pattern 160, which functions as thedrain electrode of the first switching TFT SW1 when a voltage signal isapplied to the storage electrode 110 via the driving electrode pattern170. Meanwhile, the driving electrode pattern 170 corresponds to thenode B in the circuit of FIG. 3. The driving electrode pattern 170itself functions as a drain electrode of the drive TFT D-TFT. The driveTFT D-TFT and storage capacitor Cst are connected to the drivingelectrode pattern 170, together with a second switching TFT SW2.

In this case, the first switching TFT SW1 is defined by the gate lineGL, the first active layer 130, which has a first switching channelregion 160 a at a portion thereof overlapping the gate line GL, theswitching electrode pattern 160, which is laterally connected to one endof the first active layer 130, and the data line DL, which is connectedto the other end of the first active layer. Meanwhile, as describedabove, the drive TFT D-TFT is defined by the driving gate electrode 120,the second active layer 140, which has the driving channel region 140 aat the portion thereof overlapping the driving gate electrode 120, thecurrent driving line VDL connected to the second active layer 140, andthe driving electrode pattern 170.

In this case, the driving gate electrode 120 not only functions as agate electrode of the drive TFT D-TFT, but also functions as an oppositestorage electrode of the storage capacitor Cst in accordance withoverlap thereof with the storage electrode. The driving gate electrode120 is formed to overlap with both the area where the first switchingTFT SW1 is arranged and the area where the drive TFT D-TFT is arranged.Accordingly, a separate area for formation of the storage capacitor Cstis not required, and the area of the first switching TFT SW1 and thearea of the drive TFT D-TFT share the area of the storage capacitor Cstwith each other. Thus, the circuit integration degree of the pixel areais enhanced.

Meanwhile, the second switching TFT SW2 is also included in the organiclight emitting display device. The second switching TFT SW2 is arrangedat the portion of the second active layer 140 extending to the sensingline SSL, The second switching TFT SW2 is constituted by the secondactive layer 140, which has a second switching channel at a portionthereof overlapping the sensing line SSL, the reference voltage line RLconnected to the second active layer 140, and the driving electrodepattern 170.

In addition, the first switching TFT SW1 and drive TFT D-TFT aredirectly connected without using a separate electrode. That is, theswitching electrode pattern 160, which functions as a switching drainelectrode of the first switching TFT SW1 while being arranged at anupper side, is directly connected to the driving gate electrode 120 ofthe drive TFT D-TFT, which is arranged at a lower side. Accordingly, itmay be possible to eliminate degradation of integration degree occurringin the conventional planar double connection structure.

Meanwhile, gate electrodes of the first switching TFT SW1 and secondswitching TFT SW2 are defined by portions of the gate line GL andsensing line SSL crossing the first and second active layers 130 and140, respectively. The gate line GL and sensing line SSL are arrangedover the first and second active layers 130 and 140 and, as such, havetop gate structures, respectively. On the other hand, the driving gateelectrode 120 is arranged beneath the first and second active layers 130and 140 and, as such, has a bottom gate structure. In this case, theremay be an advantage in forming the first and second switching TFTs anddrive TFT in an overlapping manner. As a result, a circuit having a highintegration degree may be formed in the pixel area. Accordingly, highresolution may be easily secured. In this case, the gate line GL andsensing line SSL are arranged over the first and second active layers,respectively, and the data line DL, reference voltage line RL andcurrent drive line VDL are arranged over both the gate line GL and thesensing line SSL.

The first active layer 130 has a “180°-rotated L” shape such that thefirst active layer 130 is laterally connected to the switching electrodepattern 160 at one end thereof while being laterally connected to thedata line DL at the other end thereof. The opposite ends of the activelayer 130 have highly doped regions 130 c formed through doping withimpurity ions at a high concentration, at lateral connection portionsthereof, respectively. A lightly doped region 130 b may be providedbetween an undoped region of the first active layer 130, namely, thefirst switching channel region 160 a, and each highly doped region 130c, in order to achieve a reduction in off-current. Provision of thelightly doped region 130 b is selective and, as such, may be omitted.

The second active layer 140 has a reversed Z″ shape. The second activelayer 140 has the drive TFT D-TFT and second switching TFT SW2 at theportions thereof overlapping the driving gate electrode 120 and sensingline SSL, respectively. The second active layer 140 is connected, atopposite ends thereof, to the current drive line VDL and referencevoltage line RL, which are arranged over the second active layer 140,respectively. The driving electrode pattern 170, which is shared as anelectrode pattern by the drive TFT D-TFT and second switching TFT SW2,is formed over a portion of the second actively layer 140 arrangedoutside the driving gate electrode 120 while being connected to thesecond active layer 140. In this case, the driving electrode pattern 170may be a common drain electrode or common source electrode of the driveTFT D-TFT and second switching TFT SW2. The electrode function of thedriving electrode pattern 170 may be varied in accordance with whetherthe conduction type of each TFT is n type or p type. The common drainelectrode or common source electrode is connected to a first electrodeof the organic light emitting diode OLED and, as such, supplies a drivecurrent to the organic light emitting diode OLED.

The second active layer 140 has highly doped regions 140 c at a portionthereof connected to the driving electrode pattern 170 protruding fromthe driving gate electrode 120 and a portion thereof connected to thedrive current line VDL. The second active layer 140 also has a highlydoped region 140 c at a portion thereof connected to the referencevoltage line: RL. Similar to the first active layer 130, the drivingchannel region of the second active layer 140 overlapping the drivinggate electrode 120 and the second switching channel region of the secondactive layer 140 crossing the sensing line SSL are undoped regions 140a. A lightly doped region 140 b may be provided between each undopedchannel region 140 a and the corresponding highly doped region 140 c, inorder to achieve a reduction in off-current. The lateral connectionbetween the driving electrode pattern 170 and the second active layer140 is provided at the corresponding highly doped region 140 c and, assuch, the driving electrode pattern 170 and second active layer 140 maybe connected at low resistance.

Meanwhile, shapes of the first and second active layers 130 and 140 arelimited to the illustrated shapes. The first and second active layers130 and 140 may have various shapes, so long as they are spaced apartfrom each other.

The organic light emitting diode OLED includes a first electrode 180, anorganic light emitting layer 190 arranged in a light emission area, anda second electrode 200 disposed on the organic light emitting layer 190.If necessary, a hole injection layer and a hole transport layer may bedisposed beneath the organic light emitting layer 190. In addition, anelectrode transport layer and an electrode injection layer may bedisposed over the organic light emitting layer 190. In this case, thehole injection layer, hole transport layer, organic light emittinglayer, electrode transport layer and electrode injection layer are madeof organic materials. Each organic material is deposited using a metalmask having an opening, in accordance with an evaporation process inwhich the organic material is deposited through the opening throughevaporation.

In addition, the organic light emitting diode OLED includes a bank 185arranged on the first electrode 180 along a boundary of the pixel area,in order to define the light emission area. The bank 185 may have adouble step structure and, as such, may have a first thickness portion1851 and a second thickness portion 1852. In the double step structure,the first thickness portion 1851 substantially functions to define thelight emission area, and the second thickness portion 1852 directlyprevents the metal mask from coining into contact with the firstthickness portion 1851 when the metal mask is bent downwards due to theweight thereof during deposition of organic materials including theorganic light emitting layer 190, thereby preventing the first thicknessportion 1851 from collapsing.

In an embodiment of the present invention, the light emission area ofthe organic light emitting diode OLED may be determined to have amaximum size, so long as light emitting colors are not mixed during thedeposition process. This is because the organic light emitting diodeOLED according to an embodiment of the present invention emits light ina top emission manner and, as such, light emission of the organic lightemitting diode OLED is achieved even though the organic light emittingdiode OLED overlaps the circuit configuration in the pixel area, indetail, light shield wiring or a light shield pattern is included in thecircuit configuration arranged beneath the organic light emitting diodeOLED. Accordingly, the light emission area may completely overlap withthe storage capacitor defined by overlapping portions of the drivinggate electrode 120 and storage electrode 110. The light emission areamay also be maximally extended at a portion thereof other than theportion overlapping the storage capacitor, so long as no color mixingoccurs between adjacent pixels. In this case, the first electrode 180may be a reflective electrode, and the second electrode 200 may be atransparent electrode, in order to achieve effective top emission.

FIG. 6 is a flowchart illustrating a procedure of manufacturing theorganic light emitting display device according to an embodiment of thepresent invention.

Hereinafter, a method for manufacturing the organic light emittingdisplay device according to an embodiment of the present invention willbe described with reference to FIGS. 4 to 6.

First, a substrate 100, which has a plurality of pixel areas arranged ina matrix, is prepared.

The substrate 100 may be further provided with a buffer layer (notshown) formed over the substrate 100.

Thereafter, an island-shaped storage capacitor 110 is formed on thesubstrate 100 at each pixel area (10S).

Subsequently, a driving gate electrode 120 is formed on the storagecapacitor 110, to overlap with the storage capacitor 110, under thecondition that a first interlayer insulating film 111 is interposedbetween the driving gate electrode 120 and the storage capacitor 110(20S). In this case, the driving gate electrode 120 has a low lateralslope of about 50° or less.

Thereafter, a first active layer 130 and a second active layer 140 areformed on the driving gate electrode 120 such that the first and secondactive layers 130 and 140 are spaced apart from each other via a firstgate insulating film 121, and overlap with the driving gate electrode120 and storage electrode 110, respectively (30S). The first and secondactive layer 130 and 140 are initially in an amorphous state. In thisstate, the first and second active layer 130 and 140 may not providesufficient mobility when used as semiconductor layers of TFTs. To thisend, the first and second active layers 130 and 140 are crystallizedusing an excimer laser before being patterned into the illustratedshapes and, as such, are formed into polysilicon layers. In thecrystallization process, heat is applied to the first and second activelayers 130 and 140 and, as such, the first and second active layers 130and 140 may be disconnected at portions thereof inclined along sideportions of the driving gate electrode 120. In order to prevent suchdisconnection, accordingly, driving gate electrode 120 has a smalllateral slope.

Thereafter, a gate line GL and a sensing line SSL are formed in parallelon the first active layer 130, to cross the first active layer 130 andsecond active layer 140, respectively, under the condition that a secondgate insulating film 141 is interposed between the first active layer130 and the gate line CL and sensing line SSL (40S).

Subsequently, an overlap region of the gate line GL and first activelayer 130 overlap each other and a peripheral region thereof, an overlapregion of the sensing line SSL and second active layer 140 and aperipheral region thereof, and an overlap region of the driving gateelectrode 120 and second active layer 140 and a peripheral regionthereof are masked by a photoresist film pattern. In this state, dopingwith high-concentration impurity ions is carried out, thereby forminghighly doped regions 130 c and 140 c (50S).

The photoresist film pattern is then asked such that the photoresistfilm pattern is left only at the overlap region of the driving gateelectrode 120 and second active layer 140. In this state, lightly dopedregions 130 b and 140 b are formed at regions exposed after the ashing,respectively.

The photoresist film pattern is removed through stripping.

Thereafter, a second interlayer insulating film 151 is formed over thesecond gate insulating film 141 including the gate line GL and sensingline SSL.

Subsequently, the second interlayer insulating film 151, second gateinsulating film 141, first active layer 130, first gate insulating film121, and first interlayer insulating film 111 are selectively removed inregions corresponding to opposite ends of the first active layer 130,opposite ends of the second active layer 140, and a portion of thesecond active layer 140 disposed between the opposite ends of the secondactive layer 140 while protruding from the driving gate electrode 120,thereby forming first to fifth contact holes CNT1 to CNT5 (60S). In thisremoval process, etching is carried out until metal surfaces areexposed. For example, in a region where one end of the first activelayer 130 is arranged, the first active layer 130 is completelyperforated such that an upper surface of the driving gate electrode 120disposed beneath the first active layer 130 is exposed, and, as such,the second contact hole CNT2 is formed. Meanwhile, in a region where thesecond active layer 140 protrudes from the driving gate electrode 120between the opposite ends of the second active layer 140, the secondactive layer 140 is completely perforated such that an upper surface ofthe storage electrode 110 disposed beneath the second active layer 140is exposed, and, as such, the third contact hole CNT3 is formed. Inaddition, in a region where the other end of the first active layer 130is arranged, the first active layer 130 is completely perforated suchthat the first gate insulating film 121 and first interlayer insulatingfilm 111 disposed beneath the first active layer 130 are etched, therebyforming the first contact hole CNT1. Similarly, in regions where theopposite ends of the second active layers 140 are arranged,respectively, the second active layer 140 is completely perforated suchthat the first gate insulating film 121 and first interlayer insulatingfilm 111 disposed beneath the second active layer 140 are etched,thereby forming the fourth and fifth contact holes CNT4 and CNT5.

In the above-described etching process, an etchant or plasma gasexhibiting similar etching rates for the insulating films and activelayers while exhibiting etching rates for metals different from theetching rates for the insulating films and active layers is used.

Thereafter, a metal is deposited over the second interlayer insulatingfilm 151. The deposited metal is then etched and, as such, a data lineDL connected to one end of the first active layer 130, and a currentdriving line VDL and a reference voltage line RL, which are connected tothe opposite ends of the second active layer 140, respectively, areformed in a direction crossing the gate line GL. In the same process asdescribed above, a switching electrode pattern 160 connected to theother end of the first active layer 130 and a driving electrode pattern170 connected to the storage electrode 110 protruding from the drivinggate electrode 120 are formed (70S).

In this case, the data line DL extends through the first active layer130 and insulating films 121 and 111 disposed beneath the first activelayer 130 in the region corresponding to the first contact hole CNT1.Similarly, the reference voltage line RL and drive voltage line VDLextend through the second active layer 140 and insulating films 1:21 and111 disposed beneath the second active layer 140 in the regionscorresponding to the fourth and fifth contact holes CNT4 and CNT5,respectively. In addition, the switching electrode pattern 160 isconnected to the driving gate electrode 120 in the region correspondingto the second contact hole CNT2, and the driving electrode pattern 170is connected to the storage electrode 110 exposed in the regioncorresponding to the third contact hole CNT3.

After formation of the first and second switching TFTs SW1 and SW2 anddrive TFT D-TFT as described above, a passivation film 161 is formedover the entire upper surface of the second interlayer insulating film141 including the data line DL, drive current line VDL, referencevoltage line RL, switching electrode pattern 160 and driving electrodepattern 170. Thereafter, a sixth contact hole CNT6 is formed to exposethe driving electrode pattern 170 of the drive TFT D-TFT (80S).

Subsequently, a first electrode 180 is formed such that the firstelectrode 180 is connected to the driving electrode pattern 170 via thesixth contact hole CNT6 (90S).

A bank 185 is formed such that the bank 180 opens the light emissionarea while partially overlapping the first electrode 180 (100S). In thiscase, the bank 185 may include a first thickness portion 1851 definingthe light emission area, and a second thickness portion 1852 formed onthe first thickness portion 1851 while having a smaller width than thefirst thickness portion 1851. The second thickness portion 1852functions as a spacer for preventing a metal mask from coming intodirect contact with the first thickness portion 1851 during an organicmaterial deposition process.

Thereafter, organic materials including an organic light emitting layer190 are deposited using a metal mask having an opening corresponding tothe light emission area.

A second electrode 200 is then formed on the organic light emittinglayer 190.

In this case, the lamination structure of the first electrode 180,organic light emitting layer 190, and second electrode 200 forms anorganic light emitting diode MED.

Meanwhile, the above-described procedures 10S to 100S may require masks,respectively. In the organic light emitting display device according toan embodiment of the present invention, a lower metal pattern shieldingthe active layers beneath the active layers is eliminated. To this end,a bottom gate structure is applied to a portion of the drive TFT mainlyand importantly acting in association with drive currentcharacteristics. That is, the driving gate electrode is first formed,and the active s are subsequently formed. Accordingly, even in theabove-described case, it may be possible to prevent the active layers ofthe drive TFT from being influenced or damaged by external lightincident thereupon at the bottom side. Thus, it may be possible toreduce two or more masking processes for pattern formation and voltageapplication when a lower metal pattern is provided, as in theconventional case.

If necessary, doping with high-concentration impurity ions andlow-concentration impurity ions into the first and second active layers130 and 140 may be carried out in separate manners before and afterformation of the gate line.

Although the second electrode 200 of the organic light emitting diodeOLED is illustrated in the circuit diagram of FIG. 3 as being grounded,the present invention is not limited thereto. A certain voltage may beapplied to the second electrode 200. The second electrode 200 may bedeposited over the entire upper surface without using a separate mask.After deposition, the second electrode 200 is connected to a commonground at a peripheral region thereof, or a predetermined common voltageis applied to the second electrode 200.

Second Embodiment

FIG. 7 is a plan view illustrating one pixel of an organic lightemitting display device according to a second embodiment of the presentinvention. FIG. 8A is a cross-sectional view taken along line II-II′ inFIG. 7.

The organic light emitting display device according to the secondembodiment of the present invention illustrated in FIGS. 7 and 8A hasfeatures in that the organic light emitting display device has a doublegate electrode structure in order to enhance mobility characteristics ofthe drive TFT, and the remaining configuration of the organic lightemitting display device is identical to that of the first embodiment.

That is, the drive TFT includes a driving gate electrode arranged, as afirst gate electrode, beneath the second active layer 140, and anauxiliary driving gate electrode 250 arranged, as a second gateelectrode, over the second active layer 140. In this case, the auxiliarydriving gate electrode 50 is disposed on the same layer as the gateline, that is, on the second gate insulating film 141, while partiallyoverlapping the second active layer 140. Accordingly, when the lightlydoped regions 130 b and 140 h are omitted in the impurity dopingprocesses, it may be possible to form the highly doped regions 130 c and140 c under the condition that channel regions are protected by the gateline, sensing line and auxiliary driving gate electrode 250, withoutusing a mask for defining a photoresist film pattern.

In accordance with formation of the double gate structure for the driveTFT, it may be possible to enhance mobility of the drive TFT andon-current characteristics, as compared to other TFTs provided in thepixel area.

Similar to the first embodiment, in the second embodiment, it may bepossible to define a storage capacitor by arranging the storageelectrode of the first embodiment on a layer different from that of thefirst embodiment under the condition that the storage electrode overlapsthe driving gate electrode. In this case, the storage capacitor is notinfluenced by arrangement of other TFTs in the pixel area and, as such,it may be possible to enhance circuit integration degree and to securehigh resolution.

In addition, the switching electrode pattern 160, which is one electrodeof the first switching TFT, is connected to the auxiliary driving gateelectrode 250. The switching electrode pattern 160 extends through thefirst active layer 130 such that the switching electrode pattern 160 isconnected to the driving gate electrode 120. Accordingly, planar longsecondary connection is not required for connection between theswitching TFT and the drive TFT and, as such, high resolution may beeasily secured. The switching electrode pattern 160 is connected to aside surface of the auxiliary driving gate electrode 250 and an uppersurface portion of the auxiliary driving gate electrode 250 in order toachieve resistance reduction while securing a sufficient connectionarea.

FIGS. 8B and 8C are cross-sectional views illustrating embodimentsmodified from the second embodiment.

If necessary, the switching electrode pattern 160 may be connected onlyto the side surface of the auxiliary driving gate electrode 250, asillustrated in FIG. 8B. Alternatively, as illustrated in FIG. 8C, in aprocess for connecting the switching electrode pattern 160 to thedriving gate electrode 120, a contact hole for exposing a portion of theauxiliary driving gate electrode 250 may be formed in addition to thecontact hole for exposing the driving gate electrode 120, in order toachieve electrical connection between an upper surface of the auxiliarydriving gate electrode 250 and the switching electrode pattern 160. Inaddition, in the case of FIG. 8C, the auxiliary driving gate electrode250 may further extend laterally, to be laterally connected to theswitching electrode pattern 160. Thus, the lateral connection and theconnection through the contact hole may be simultaneously achieved.

Hereinafter, effects of the organic light emitting display deviceaccording to an embodiment of the present invention will be described.

FIG. 9 is a graph depicting V_(g)-I_(d) characteristics exhibited whenthe drive TFT has a top gate structure and when the drive TFT has abottom gate structure.

In FIG. 9, transfer curve characteristics are depicted. Referring toFIG. 9, it can be seen that, when the voltage applied to the drivinggate electrode increases, the bottom gate structure has slightly higherdrive current Id than that of the top gate structure.

FIG. 10 is a graph depicting V_(d)-I_(d) characteristics exhibited whenthe drive TFT has a top gate structure and when the drive TFT has abottom gate structure.

In FIG. 10, output curve characteristics are depicted. Referring to FIG.10, it can be seen that, when a gate voltage is sequentially increasedfrom 0V to 4V in the case in which the gate electrode of the drive TFTis of a bottom gate type, drive current I_(d) in the bottom gatestructure is almost saturated in accordance with a voltage V_(d) of thedrain electrode, whereas drive current I_(d) in the top gate structureexhibits non-linear increase in accordance with the voltage V_(d) of thedrain electrode. This means that, in the case of the top gate structure,output characteristics thereof exhibit unstableness in accordance with avariation in the voltage V_(d) of the drain electrode. Accordingly,superiority of the bottom gate structure exhibiting relatively stableoutput characteristics may be verified.

That is, in addition to the above-described advantages, namely, highintegration and high resolution, the organic light emitting displaydevice according to an embodiment of the present invention hasadvantages in that the drive current exhibits saturationcharacteristics, and kink effects are stabilized, as the configurationof the drive TFT, which has direct influence on drive currentcharacteristics, among elements included in the pixel area, has a bottomgate structure.

In addition, an overlap area of the storage capacitor is secured by adual gate structure and, as such, high resolution may be secured.

In accordance with the organic light emitting display device accordingto an embodiment of the present invention and the method formanufacturing the same, the following effects are provided.

First, for formation of the storage electrode, no separate space isprovided, except for spaces given for TFTs. The area overlapping one ofthe TFTs, in particular, the area overlapping the driving gate electrodeof the drive ITT is used as an opposite storage electrode, and a storageelectrode is provided at a layer different from that of the driving gateelectrode such that the storage electrode overlaps the driving gateelectrode, to define the storage capacitor in a region where the storageelectrode overlaps the driving gate electrode. Accordingly, it may bepossible to obtain a sufficient storage capacitance without significantinterference with arrangement of the TFT in a pixel area.

Second, a bottom gate electrode exhibiting excellent drive currentsaturation characteristics and stable kink characteristics is applied tothe drive TFT and, as such, reliability of a pixel circuit in theorganic light emitting display device may be enhanced.

Third, connection between the switching TFT and the drive TFT isachieved by extending one electrode of the switching TFT to the drivinggate electrode through an active layer, to be connected to the drivinggate electrode. Accordingly, it may be possible to omit a planarconnection area for connection between the TFTs and, as such, there areadvantages in association with high integration and high resolution.

Fourth, the drive TFT is provided with the driving gate electrodearranged beneath the active layer, whereas the switching TFT is providedwith a gate line or a sensing line, which is arranged over the activelayer. In this regard, the gate electrodes (lines) of the TFTs arearranged at different layers, respectively. According, if necessary, adouble gate electrode may be easily applied to a TFT having highmobility characteristics.

Fifth, a lower metal pattern used in a top gate structure to shieldactive layers beneath the active layers may be eliminated. A bottom gatestructure may be applied to a portion of the drive TFT mainly andimportantly acting in association with drive current characteristics.That is, the driving gate electrode is first formed, and the activelayers are subsequently formed. Accordingly, even in the above-describedcase, it may be possible to prevent the active layers of the drive TFTfrom being influenced or damaged by external light incident thereupon atthe bottom side. Thus, it may be possible to reduce two or more maskingprocesses for pattern formation voltage application when a lower metalpattern is provided, as in the conventional case.

Sixth, in associated with the drive TFT, active layers may be formedover a driving gate electrode after formation of the driving gateelectrode. Accordingly, a channel region may be defined irrespective ofthe shape of the driving gate electrode and, as such, the degree ofdesign freedom may be increased.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1.-16. (canceled)
 15. An organic light emitting display devicecomprising: a substrate having a plurality of pixels in a matrix; astorage electrode at each of the pixels on the substrate; a driving gateelectrode over the storage electrode via a first interlayer insulatingfilm, wherein the driving gate electrode overlaps the storage electrode,to define a storage capacitor; first and second active layers over thedriving gate electrode via a gate insulating film, wherein the first andsecond active layers are spaced apart from each other while overlappingthe driving gate electrode and the storage electrode, respectively; agate line and a sensing line over the first active layer via a secondgate insulating film extending in parallel, to cross the first andsecond active layers, a data line, a current driving line and areference voltage line extending in a direction crossing the gate line,arranged over the gate line and the sensing line via a second interlayerinsulating film while, wherein the data line is connected to one end ofthe first active layer, the current driving line and the referencevoltage line are connected to opposite ends of the second active layer,respectively; and a switching electrode pattern and a driving electrodepattern arranged on a second interlayer insulating film, wherein theswitching electrode pattern and the driving electrode pattern aredisposed on the same layer as the data line, the switching electrodepattern is connected to the other end of the first active layer, and thedriving electrode pattern is connected to a portion of the storageelectrode protruding from the driving gate electrode.
 16. The organiclight emitting display device according to claim 15, further comprising:an auxiliary driving gate electrode arranged on the second gateinsulating film overlapping the driving gate electrode, wherein theauxiliary driving gate electrode is connected to the switching electrodepattern.
 17. A method for manufacturing an organic light emittingdisplay device, comprising: preparing a substrate having a plurality ofpixels in a matrix; forming a storage electrode at each of the pixels onthe substrate; forming a driving gate electrode over the storageelectrode via a first interlayer insulating film such that the drivinggate electrode overlaps the storage electrode, to define a storagecapacitor; forming first and second active layers over the driving gateelectrode via a gate insulating film such that the first and secondactive layers are spaced apart from each other while overlapping thedriving gate electrode and the storage electrode, respectively; forminga gate line and a sensing line over the first active layer via a secondgate insulating film such that the gate line and the sensing line extendin parallel, to cross the first and second active layers; and forming adata line, a current driving line and a reference voltage line over thegate line and the sensing line via a second interlayer insulating filmsuch that the data line, the current driving line and the referencevoltage line extend in a direction crossing the gate line, the data lineis connected to one end of the first active layer, and the currentdriving line and the reference voltage line are connected to oppositeends of the second active layer, respectively, and forming a switchingelectrode pattern and a driving electrode pattern in the same layer asthe data line on a second interlayer insulating film, wherein theswitching electrode pattern is connected to the other end of the firstactive layer, and the driving electrode pattern is connected to aportion of the storage electrode protruding from the driving gateelectrode.